16 



BULLETIN 105, U. S. DEPARTMENT OF AGRICULTURE. 



bitumen showed a slight tendency to bleed. The necessary repairs 

 were rapidly made by the patrolman, but as section markers had not 

 then been placed, his costs could not be distributed. When the 

 sections had once been put in thorough repair they were permitted to 

 wear without further attention, with the results above given. 



The exposed concrete surfaces as a whole presented a smooth, 

 uniform texture, and there was apparently no difference in wear 

 between the plain cement and oil-cement concrete. The addition of 

 hydrated lime has had no noticeable effect on the concrete. This 

 section can not be distinguished from the others and has developed 

 four cracks in a total length of 260 feet. Transverse cracks developed 

 at varying intervals throughout the sections, and the average distance 

 between cracks is shown in Table 18, which is based on observations 

 made November 5, 1913. It should be noted that the cracks in the 

 sections which had been surface-treated with bituminous materials 

 include those which were noted before the surface treatment was 

 applied as well as those which have since been noted through cracking 

 of the bituminous surface. 



Table 18. — Average distance between cracks in concrete road of Chevy Chase, Md. 



Character of pavement. 



Length. 



Average 

 distance 



Concrete. 



Aggregate. 



between 

 cracks. 



Surface coated with bituminous materials: 





Feet. 

 660 

 580 

 230 

 370 



425 

 600 

 300 

 210 

 260 

 290 



Feel. 

 45 



Do 



Limestone 



.do 



145 

 115 



Do 





50 



Surface exposed: 



do 



61 



Do 



Limestone 



Trap 



Limestone 



100 



Do 



Oil-cement ; 



Do 



40 

 105 



45 



Do 



Trap 



60 









It will be noteel from the foregoing table that cracks have developed 

 at a greater average elistance where a limestone aggregate was used, 

 and at the last inspection there wero still two sections of the limestone 

 concrete each 140 feet in length without a crack. When the edges of 

 any cracks began to wear excessively, the cracks were rilled with 

 the water-gas tar preparation No. 1 and sand. The results of this 

 treatment have thus far proved entirely satisfactory. 



The measurements referred to in Circular No. 99 are being con- 

 tinueel, and it is probable that interesting results will be reported in 

 the near future. 



No difference was noted in the character of the various sections of 

 brick pavement. The grouted surface had practically all worn off, 

 and it was observed at a few places throughout the length of the sec- 



